Correlation of the cyclic cracked round bar test and hydrostatic pressure test for unplasticized polyvinylchloride

Abstract

The applicability of the cracked round bar (CRB) test according ISO 18489 for the characterization of slow crack growth (SCG) in unplasticized polyvinylchloride (PVC–U) was analyzed by testing three PVC-U pipe compounds with different molecular mass, represented by different intrinsic viscosity numbers (K-values). The tests were conducted at lower stress loading ranges than recommended by the standard. The SCG resistance showed a clear dependency on the K-value resulting in a higher crack resistance with increasing K-value. Moreover, the results of the CRB tests were correlated to hydrostatic pressure tests of PVC-U pipe grades with different K-values. A clear linear correlation between the results of both methods was established, thereby demonstrating a significant acceleration of testing times with the CRB test. With a special focus on EN 1401–1, it was elaborated that the requested minimum failure resistance of 1′000 h in the hydrostatic pressure test at T = 60 °C correlates to 97′000 cycles, or 2.7 h, respectively, in the CRB test at T = 23 °C.

Keywords

• Slow crack growth
• Fracture mechanisms
• Stress intensity factor
• PVC-U
• Pipe
• Material ranking